The book is set in a world of roughly the same technological level as the Napoleonic Wars. The protagonist is Emily Marshwic, the middle sister of a family of proud lineage but lately diminished wealth. Emily's country, the kingdom of Lascanne, is engaged in a war with neighbouring Denland, which was an ally until a revolution in Denland overthrew its monarchy. To stop the ravaging hordes of bloodthirsty revolutionaries from plunging Lascanne into the same chaos, the good and noble king of Lascanne leads his people in a heroic defence of their beloved country or that's how most people in Lascanne see it, anyway. The only person who'll present things to Emily in a different light is Mr. Northway, an old enemy of her family and everyone knows how corrupt and cynical he is, so she's not about to believe him.
The authorities perpetually claim the war is "almost won", and yet, the army always seems to need more and more people conscripted into it. Emily's family does its bit first her brother-in-law goes to war, then her brother. But when the word eventually comes that one woman from every household will be conscripted too, Emily herself marches off. The battlefield is a hellish swamp, the military leadership doesn't inspire much confidence, and the Denlanders aren't the ill-disciplined rabble people say and on top of it all, the authorities may have been dishonest about more than just the progress of the war.
The book contains examples of:
- 0% Approval Rating: Mr. Northway, Mayor-Governor of Chalcaster, is widely unpopular everyone knows him to be corrupt, and the aristocrats who are just as bad nevertheless view him as a shabby commoner who they'd rather not have at parties. Emily has particular reason to dislike him, but finds that he's used to being disliked and doesn't take it amiss he even gives her his blessing. She eventually decides that he's not so bad... but his approval rating with everyone else is likely still low, since he's now working for the victorious foreign occupiers, mitigating their rule while enduring the inevitable unpopularity.
- The Alcoholic: Father Burnloft, the priest attached to the army in which Emily is sent to serve, is habitually drunk. It may simply be a consequence of all the death he's seen, but soldiers who've seen just as much and now have to listen to him stagger through the funeral service for their dead comrades don't necessarily have much sympathy.
- An Arm and a Leg: Emily's brother-in-law, Tubal, finishes the war minus a leg. He's not as bitter about it as he might be after all, a lot of the people he fought beside got worse.
- Bittersweet Ending: Emily survives, and at least some of the people she cares about survive too (including the one she had developed feelings for). As a bonus, the person responsible for the war is dead. However, this occurs against the backdrop of her country having lost the war, and now being under foreign occupation. (This isn't as big a downer as might have been assumed at the start of the book, though, since it turns out the foreigners weren't the ones who started it and aren't the crazy anarchists they were portrayed as.)
- Courier: Penny Belchere is an official military courier for the kingdom of Lascanne, and is the first woman most of the characters have seen in army uniform. It's an early sign that Lascanne is running out of male conscripts and is thinking about how women can be put in military roles, which presages Emily's own conscription. (Penny Belchere herself shows up again a number of times, including once when her supposedly non-front-line role doesn't stop her getting captured.)
- Dangerous Deserter: With most able-bodied men away fighting in the war, a gang of men who theoretically should be fighting in the war see an opportunity to prey on undefended lands well behind the front lines. Wealthier households such as Emily's are prime targets, especially when they contain Emily's sister Alice, who's unwise enough to be lured a supposed romantic rendezvous by a hostage-seeking bandit.
- Deconstruction: The novel deconstructs Politically Correct History and does a realistic take on the concept of female soldiers fighting alongside men in a historical period where this wouldn't have been the case. Lascanne is depicted as a very patriarchal nation with Stay in the Kitchen attitudes being the norm. Guns of the Dawn explores the question of what would drive a sexist country like Lascanne into conscripting women for their army. The answer? Total desperation. It turns out that the kingdom is on the receiving end of a Curb-Stomp Battle in a Hopeless War against a Technologically Advanced Foe. The military is facing a severe Mook Depletion and all of Lascanne's able-bodied men are either dead or worn out by the fighting against Denland. The kingdom essentially has no choice but to enlist women, many of whom are unprepared for war and only given minimal training.
- De-Power: Warlocks get their powers from their king, so when Denland's monarchy fell, it was left without warlocks to bolster its army in the war against Lascanne. This kind of de-powerment becomes unexpectedly useful at the end of the book, when Giles Scavian, a warlock of Lascanne captured when the Denlanders won the war, is rendered harmless and therefore safe thanks to Emily killing her own country's king.
- Foolish Sibling, Responsible Sibling: The Marshwic family has Mary and Emily, who tend towards the serious, and Alice, who is interested in balls and dresses despite the family not really having the money to support that kind of lifestyle any more. It's played with a bit, though, in that Alice's determination to lead a properly aristocratic social life is revealed to be partly motivated by her belief that a good marriage is the only way to alleviate the financial troubles that keep the others so glum. On the other hand, her good motivations don't make her any smarter, as proven when she runs away to meet someone who turns out to be a ransom-seeking outlaw.
- Gaslamp Fantasy: The technology level is about that of the Napoleonic Wars, but it exists alongside fantasy elements most prominently, warlocks empowered by kings.
- Going Native: The armies of Lascanne and Denland are fighting through a swamp, and Mallen, the chief scout on the Lascanne side, has spent so long there that his sympathies lie more with the swamp's "indigines" than with either army. He helps his own side in the fight, but always in a way which doesn't conflict with his apparently higher priority of keeping the indigines out of harm's way.
- The Good King: King Luthrian IV of Lascanne is widely adored by his subjects, and his call to arms against invading republican revolutionaries from Denland is well supported. It doesn't hurt that he also has a good amount of Prince Charming about him, being young, handsome, unmarried, and a good dancer as Emily personally discovers. In the end, it turns out that the war which he portrays as a heroic defence was actually the result of his own failed attempt to annex Denland by assassinating its king. He shows no remorse for the countless deaths his scheme caused, even after Denland has won and he's a fugitive. In fact, he has the gall to expect Emily to help raise rebellion in his name instead, she shoots him.
- Impoverished Patrician: The Marshwic family was once fairly wealthy, but a series of misfortunes left it in dire financial straits (and led to the head of the family shooting himself). The family blames much of this on their old rival, Mr. Northway the fact that his fortunes went in the opposite direction (he's now governor of the city) is, to the Marshwics, a great injustice that will surely be corrected as soon as the king learns how wicked Mr Northway is. Mr Northway, while not denying his own corruption, says that Emily's late father was just as bad and that the king cares more for obedience than integrity. He's right.
- I Never Got Any Letters: Mary is upset that she hasn't had much correspondence from her husband, Tubal, who is away at war. When Emily ends up at the front and meets Tubal, she learns the reason the army censors letters "to preserve morale", so Tubal knew that any letters he sent would just disappear unless he lied to Mary about what things were like.
- In Medias Res: The story starts with Emily seeing one of her comrades/friends killed in battle; it then goes back to Emily's life before being conscripted and gradually works its way up to that point before continuing. (As such, we know that Elise's death is a Foregone Conclusion when Emily first befriends her.)
- Mad Doctor: The enemy army is under the command of the notorious "Dr. Lam", said to be a physician who rose to power in the chaos of revolution and who now enjoys dissecting captured prisoners. When Emily gets captured, she's taken to see him. It turns out that not only is Dr. Nathanial Lammegeier not a medical doctor (he's an engineer), he's also one of the nicest characters in the book. This isn't the biggest falsehood believed about the Denlanders and their "bloodthirsty revolution", either.
- The Quisling: After the war is over, Mr. Northway, formerly Mayor-Governor of Chalcaster for the king of Lascanne, continues in that role despite the change in leadership. His motivations are reasonably good someone has to be in charge, and continuity of government will avert dangerous instability. It doesn't do wonders for his public image, but then, people didn't think much of him anyway.
- Reality Ensues:
- It's noted that being a Military Mage means that the enemy will make killing you their number one priority. Hence why they don't wear robes, which would only make them stick out from the other troops.
- Much like in Wonder Woman (2017), Denland's secret weapon isn't something fantastical like Applied Phlebotinum or Magitek. It's a new invention Dr. Lam refers to as "the rifle". It turns out that a firearm with more accuracy and range than your enemies is just as dangerous as any Military Mage. Moreso, since, unlike Lascanne's warlocks, rifles can be mass-produced.
- The Remnant: By the end of the book, the army in which Emily is fighting has become this without realising it. Fighting in an inaccessible area, they don't realise that their forces elsewhere have collapsed and that they are now encircled. They're persuaded to surrender, but still gain a lot of praise from the citizenry for being the last survivors which becomes important when the fugitive king tries to use Emily, now as much of a war hero as you can get in a defeated country, as the centre of an uprising. The king's own band, however, is not so much a remnant of his old forces as a new gang of bandits he has recruited through bribes.
- Simple, yet Awesome: For Denland, inventing the rifle turns out to be this. By milling a spiral groove into the barrels of their muskets and using leather-encased musket balls as ammunition, they create a gun which can shoot at a long-range, is far more accurate than any other firearm of their time, and turns the war with Lascanne into a shooting gallery.
- Why Can't I Hate You?: Mr. Northway is (by his own admission) corrupt and self-interested, and his rivalry with the Marshwic family led to its current impoverished status and the suicide of Emily's father. Emily starts out hating him, and makes this clear to him. However, this openness of disregard actually enables them to converse more freely and honestly than if they were pretending to be polite friends, and Emily finds that she's glad to have someone to correspond with who treats her as an equal adversary, doesn't assume he can trick or patronise her, and isn't put off by her barbs and criticisms.